Vat-based additive manufacturing with dispensed material

ABSTRACT

Methods of creating additive manufactured parts include providing a first composition in a vat, where the first composition is a liquid with a first viscosity. A build platform is placed adjacent to and submerged under a top surface of the first composition. A second composition is dispensed on the top surface, the second composition having a second viscosity and being dispensed in a shape area according to a part to be created. The top surface is illuminated to expose the first composition and second composition to light having a polymerization wavelength, thereby causing polymerization of at least one of the first composition or second composition. In some embodiments, the first composition is a base resin that is absent of a photoinitiator, and the second composition is a photoinitiator solution. The photoinitiator solution may have a second viscosity that is less than the first viscosity of the base resin.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.63/086,829, filed on Oct. 2, 2020 and entitled “Vat-Based AdditiveManufacturing with Dispensed Material”; the contents of which are herebyincorporated by reference in full.

BACKGROUND

Additive manufacturing (i.e., 3D printing) has become an extremelypopular method for producing parts, from prototypes to commercialproduction. There are many types of additive manufacturing systems andmethods that have been developed. Some types utilize a vat containing aphotosensitive polymer (i.e., photopolymer), where layers of the 3Dprinted part are grown upon each other within the vat. The photopolymercross-links and hardens upon exposure to photopolymerization wavelengthsof light, changing the liquid resin into a solid polymeric material.These photoreactive 3D printing systems typically include a resin pool,an illumination system, and a print platform, where the illuminationsystem projects an image into the resin pool causing a layer of apolymeric object to be formed on the print platform. The print platformthen moves the printed layer out of the focal plane of the illuminationsystem, and then the next layer is exposed (i.e., printed). Some systemsuse a “top-down” approach where the light exposes an upper surface ofthe resin, and then the print platform moves down into the vat so thatthe next layer can be built. Other systems are “bottom-up” where thelight is projected through a transparent bottom surface of the resinpool, and then the print platform moves up, away from the bottomsurface, as the part continues to be formed.

Stereolithography (SLA) 3D printing employs a point laser or lasers thatmove around a 2D plane in a rasterized manner to create a pattern layerin the resin. Other conventional systems use digital light processing(DLP) or similar imaging in order to expose an entire layer at once withimproved speed. However, one problem that arises with conventionaladditive manufacturing systems utilizing DLP is that as the layer sizeincreases, the pixel size increases proportionally. The result is adecrease in the resolution of the final part, which will negativelyaffect part accuracy and surface finish. This also has the negativeeffect of reducing the projected energy density, which slows down theprint process further as each layer needs a longer exposure time.Therefore, as DLP systems are used for larger layer sizes, thetheoretical advantage that full layer exposing achieves over othermethods is reduced.

Other types of additive manufacturing create a printed part in anopen-air environment rather than in a vat. In one example, polymers areinkjet-printed onto a substrate and then exposed to radiation such asultraviolet (UV) light to initiate photopolymerization. The polymers maybe two different compounds that are capable of polymerizing when mixedtogether. In another example, a bed of powdered material is supplied ona substrate, and a fusing agent is dispensed by inkjetting at locationswhere the material is desired to be fused together. The material bed isexposed to energy such as light or heat, causing the material to fusetogether where the agent is present.

SUMMARY

In some embodiments, a method of creating additive manufactured partsincludes providing a first composition in a vat, where the firstcomposition is a liquid with a first viscosity. A build platform isplaced in the vat, submerged under a top surface of the firstcomposition. A second composition is dispensed on the top surface of thefirst composition, the second composition having a second viscosity andbeing dispensed in a shape area according to a part to be created. Thetop surface is illuminated to expose the first composition and thesecond composition to light having a polymerization wavelength, therebycausing polymerization of at least one of the first composition or thesecond composition.

In some embodiments, a method of creating additive manufactured partsincludes providing a base resin in a vat, where the base resin has afirst viscosity and is absent of a photoinitiator. A build platform isplaced in the vat, submerged under a top surface of the base resin. Aphotoinitiator solution is dispensed on the top surface of the baseresin, the photoinitiator solution being dispensed in a shape areaaccording to a part to be created. The photoinitiator solution has asecond viscosity that is less than the first viscosity of the baseresin. The top surface is illuminated to expose the photoinitiatorsolution and the base resin to light having a polymerization wavelength,where the light causes polymerization only where the photoinitiatorsolution was dispensed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an additive manufacturing system, in accordancewith some embodiments.

FIG. 2 is a diagram of an additive manufacturing system having apage-wide illumination source, in accordance with some embodiments.

FIG. 3 is a diagram of an additive manufacturing system having a blanketexposure illumination source, in accordance with some embodiments.

FIGS. 4A-4B show stages of forming an additively manufactured part, inaccordance with some embodiments.

FIG. 5A is an outline of a desired shape for a layer of an additivelymanufactured part, and FIG. 5B is a diagram illustrating variations of adispensed material in the shape, in accordance with some embodiments.

FIG. 6 is a flowchart of additive manufacturing methods, in accordancewith some embodiments.

FIGS. 7A-7B show chemical equations for thiol-ene reactions, as known inthe art.

FIGS. 8A-8B illustrate dispensing of a photoinitiator and apolymerization blocking material at locations in a layer, in accordancewith some embodiments.

FIGS. 9A-9C show examples of dispensing heads, in accordance with someembodiments.

FIGS. 10A-10H are diagrams of various configurations of dispensing headsand illumination sources, in accordance with some embodiments.

FIGS. 11A-11C are illustrations of additive manufacturing systems thatutilize an electric field system, in accordance with some embodiments.

FIG. 12 is a plan view showing the use of dispensed droplets to controlan orientation of fibers in a vat, in accordance with some embodiments.

FIG. 13 is a flowchart of further additive manufacturing methods, inaccordance with some embodiments.

DETAILED DESCRIPTION

The present disclosure describes vat-based additive manufacturingtechniques in which certain materials are selectively dispensed onto thetop surface of a liquid substance in the vat. The vat is a tank or tubthat is used to hold liquid. Embodiments provide on-demand deliverysystems for dispensing materials such that reactants/components comeinto contact with each other in the vat to form additive manufacturedparts. In some embodiments, a substance is dispensed on the surface of aphotopolymerizable content that is in the vat, selectively promotingpolymerization only in the areas where the substance is delivered. Insome embodiments, the dispensed substance may be a reaction activatorsuch as a photoinitiator solution that is precisely added into the vatmaterial, and the vat material does not include a photoinitiator. Afterbeing dispensed in the vat, the photoinitiator absorbs a polymerizationactuation energy such as ultraviolet (UV) light, such that the materialis cured only where the photoinitiator is present. In some embodiments,a first reactant of a chemical reaction can be used as the vat materialand a second reactant that will react with the first reactant forpolymerization (e.g., in the presence of UV light) can be dispensed,such as thiols and/or -enes. The term “-enes” refers to chemicalcompounds containing an ene functional group. In some embodiments, thevat material need not contain polymerizable content. For example, thevat material can be an inert medium such as water, glycerin, or gel withdesired physical/chemical properties, and polymerizable components aredispensed onto the inert medium (e.g., liquid, gel or other fluid-likesubstance) in the vat.

Embodiments of the present disclosure provide advantages for additivemanufacturing such as improving the ability to scale up 3D printed partsizes while achieving high resolution quality. Embodiments of thepresent disclosure also provide an advantage of improving the shelf-lifeof vat materials. For example, keeping the photoinitiator separate fromthe other resin ingredients increases the shelf-life of the resiningredients and provides the ability to easily store thenon-photoinitiator materials in areas containing light. In otherexamples, embodiments provide the ability to deliver and mix chemicallylabile components at the desired moment to circumvent shelf-life issues,such as in thiol-ene material systems. Conventional vat-based systemsthat offer larger build areas for scaled-up part sizes, in contrast,present problems for controlling and managing vat life. Unusable resinresults in high scrap costs, such as tens or hundreds of thousands ofdollars if the resin in a vat is compromised.

Conventional vat-based 3D printing solutions, especially those involvingDLP or projection-based systems, also tend to have thermal issuesinvolving unintended over-cure in hot areas, resulting in print defects.Thermal issues are typically a result of non-uniformities of the UVlight source (e.g., hot spots) and cross-sectional area density of thegeometry being printed. Higher cross-sectional area density causes hotspots due to the exothermic reactions from the polymerization process.To address the thermal issues, conventional methods usually slow downprinting processes by either reducing the UV light source intensity oradding additional delays throughout the print process. Slowing down theprint process reduces productivity and increases cost. Embodiments ofthe present disclosure address thermal issues in a different manner, byprecisely varying and/or controlling the amount, concentration, and/ortype of a dispensed substance (e.g., photoinitiator or other component)as needed.

FIGS. 1-3 show isometric views of additive manufacturing systems, inaccordance with some embodiments. The systems combine a vat-based formatwith dispensing of additional materials onto the vat material that fillsthe vat. Various embodiments of vat materials and dispensed materialsshall be described in relation to FIGS. 1-3, where a vat materialcontained in the vat shall also be referred to as a first composition. Adispensing system such as a jetting head used in inkjet printingdispenses a material onto the vat material, where the dispensed materialshall be referred to as a second composition. In this disclosure thematerials in the vat and being dispensed may also be referred to ascompositions, substances, reactants, and components. Also, thedispensing of material will primarily be described in terms of inkjetdispensing (jetting). However, other types of dispensing techniques arealso applicable.

Conventional photoreactive resins are made of monomer, oligomer,photoinitiator, and other materials, where a key ingredient that makesthe resin polymerize and sensitive to light is the photoinitiator. Insome embodiments of FIG. 1, a first composition 115 held in a vat 110 isa resin base material (which may also be referred to in this disclosureas a base resin), where the resin base material is absent of aphotoinitiator. That is, the base resin is a composition of substancesthat will be polymerized into a hardened part but lacking a componentthat would allow the polymerization to occur. A dispensing head 120(e.g., inkjet printing head, syringe/pump-type or other) preciselydispenses photoinitiator in liquid form as a second composition 140 ontoa top surface 118 of resin base material in the vat 110. Although thisembodiment shall be described as dispensing only photoinitiator,embodiments may include dispensing more than one material from thedispensing head 120 (or from more than one dispensing head), as shall bedescribed throughout this disclosure. Furthermore, although FIGS. 1-3shall primarily be described in terms of dispensing a photoinitiatorsolution onto a vat material that is absent of a photoinitiator, FIGS.1-3 may apply to any of the combinations of dispensed materials and vatmaterials described throughout this disclosure.

In the embodiment of FIG. 1, the dispensing head 120 has a dispensingarea 122 that covers only a portion of a width (Y-direction) and aportion of a length (X-direction) of the top surface 118. Consequently,the dispensing head 120 may dispense the photoinitiator over the entiretop surface 118 by moving in, for example, a raster pattern (e.g.,moving the head side to side in the X-direction to form lines,progressing from top to bottom in the Y-direction). The shape 150 formedby where the photoinitiator droplets were dispensed is the pattern areaof a layer of the additive manufacturing part being printed. Theadditive manufacturing part is formed on a build platform 160 which issubmerged in the vat 110. The build platform 160 is adjacent to andunderneath the top surface of the resin base when the initial layer of apart is being made, and moves down (negative Z-direction) into the firstcomposition 115 as subsequent layers are continued to be formed. Forclarity, the components illustrated in figures throughout thisspecification may not necessarily be drawn to scale. For example, inFIG. 1 the distance between the platform 160 to the top surface 118 andthe distance between the dispensing head 120 from the top surface 118are larger than what actually may be used.

The resin material and dispensed photoinitiator are then exposed to awavelength of light from an illumination source 130, which causespolymerization in selective areas constrained to where thephotoinitiator is present. The polymerized layer adheres to the buildplatform 160 as in known vat-based processes. The illumination source130 may be a UV light source or any other source that produces curingwavelengths that are reactive with the photoinitiator and base resin.For example, in some embodiments, the resin may be photosensitive towavelengths of illumination from about 200 nm to about 500 nm, or towavelengths outside of that range (e.g., greater than 500 nm, or from500 nm to 1000 nm). In the embodiment shown in FIG. 1, the illuminationsource 130 emits light having an area 132 at least similar in size to orgreater than the size of the dispensing area 122 of the dispensing head120. The illumination source 130 may emit light in a pass subsequent tothe jetting head, where the illumination source 130 is moved by amechanism separate from a mechanism that moves the dispensing head 120.Alternatively, the illumination source 130 may be moved simultaneouslywith the dispensing head 120, such as by having the illumination source130 attached to the same movement mechanism as the dispensing head 120.

FIG. 2 is an isometric view of another additive manufacturing system 200which utilizes a “page-wide” array approach, where a dispensing headspans a width “W” of the vat (or at least as wide as the build platform)and moves across a length “L” of the vat to expose the resin toradiation on a single pass. The system 200 includes similar componentsas system 100—a vat 210 filled with a first composition 215 (e.g., aresin base material without photoinitiator), a dispensing head 220(e.g., a jetting head), a light source 230 (e.g., UV light source), anda build platform 260 that is submerged under a top surface of the resinbase. The build platform 260 is adjacent to the top surface of the resinbase when the initial layer of a part is being made. The dispensing head220 begins at one end of the vat and moves across the length(X-direction). Because the dispensing head 220 spans the entire width Wof the vat 210 at once, dispensing second composition 240 in selectedareas according to the print pattern, only one pass across the vatlength L is needed. Photoinitator droplets of second composition 240 arepresent in an area of shape 250 after the pass is completed. Thedispensing head 220 may have multiple dispensers (e.g., nozzles) tocover the width of the jetting head, such as in the form of a linear,staggered or offset array (e.g., see FIGS. 9A-9C). In this embodiment ofFIG. 2, the UV light source 230 is also a page-wide array that isincorporated into the same mechanism as the jetting head 220, allowingthe dispensing (e.g., jetting) and the curing to be performed in thesame pass to form a polymerized layer of the printed part. In otherembodiments, the light source 230 and dispensing head 220 may bedecoupled from each other, such that the light source 230 passes overthe vat 210 separately from and after the dispensing head 220.

FIG. 3 shows another embodiment in which the illumination source isconfigured to illuminate an area as large as the entire top surface areaof the vat, to expose the entire top surface of the first composition(e.g., resin) to light at one time (e.g., a blanket exposure). System300 includes similar components as system 100—a vat 310 filled with afirst composition 315 (e.g., a resin base material withoutphotoinitiator), a dispensing head 320 (e.g., a jetting dispenser), anda light source 330 (e.g., UV). A build platform that is submerged undera top surface of the resin base is not shown in this illustration. Thedispensing head 320 is shown as a page-wide array in this embodimentsimilar to dispensing head 220 of FIG. 2. However, dispensing head 320may also be configured similar to dispensing head 120 of FIG. 1 thatdispenses material only in a discrete area. The light source 330 of FIG.3 is stationary, covering approximately the entire top surface of thevat 310, or at least an area as large as the build platform. In thisembodiment, the dispensing head 320 first moves along the Y-axis. Afterthe dispensing head 320 has completed its full pass, depositing thesecond composition (e.g., photoinitiator) in the shape 350, the lightsource 330 is activated to cure the first composition and/or secondcomposition in the vat 310.

In further embodiments, more than one type of light source may beutilized, where one light source (e.g., light source 130 or 230) moveswith the dispensing head and the other is stationary (e.g., light source330). The multiple light sources can be activated at different timesfrom each other, such as one light source being activated before, duringor after the activation of another light source. Further configurationsof dispensing heads and light sources are described in FIGS. 10A-10H.

FIGS. 4A-4B show a progression of forming layers of an additivelymanufactured part, in accordance with some embodiments. In these sidecross-sectional views of an additive manufacturing system 400, a vat 410is filled with a first composition 415 (e.g., a resin base materialwithout photoinitiator). A dispensing head 420 and a light source 430are positioned over a top surface 418 of the first composition 415,moving together in a print direction indicated by arrow 470. Dispensinghead 420 and light source 430 may take the form of any embodimentsdisclosed herein, such as raster, page-wide or blanket coverage. Thedispensing of the second composition 440 and activation of light source430 may be performed approximately simultaneously (immediately after thesecond composition is dispensed) or sequentially (having a delay timefrom when the dispensing occurs and when the light source is activatedat the dispensed location). Activation of the light source “immediately”after dispensing can be considered in this disclosure to account for thetime for the dispensed material to travel to the surface of the vatmaterial that is a particular distance away from the dispensing head.For example, in some embodiments the dispensing head and top surface ofthe vat material may be 1 mm to 3 mm apart and the dispensed materialmay have a jetting velocity of about 5 m/s to 20 m/s. The travel timefor the dispensed material to reach the vat material in these scenariosmay range from approximately 0.05 ms (1 mm distance at 20 m/s) to 0.6 ms(3 mm at 5 m/s), such as approximately 0.16 ms (2 mm at 12.5 m/s). Thus,“immediately” or “simultaneously” may be considered as activating alight source less than a millisecond (e.g., on the order ofmicroseconds) after the dispensing is initiated. In some embodiments aspecifically designed delay time (elapsed time) between the dispensingand the curing (activating the light source) may be used, where thedelay time may range from, for example, microseconds to milliseconds, ormilliseconds to seconds, or milliseconds to minutes, or microseconds tohours depending on the chemistry of the reactants being used.

FIG. 4A depicts formation of an initial layer 450 of an additivemanufactured part, where build platform 460 is positioned adjacent toand just underneath the top surface 418. For example, an upper surfaceof build platform 460 can be from 0 to 1000 μm below the surface 418during the formation of the initial layer. The dispensing head 420deposits second composition 440 (e.g., photoinitiator) in a shapeaccording to the first layer 450 of the part being created. Light energyis absorbed in the pattern areas where the photoinitiator is presentwith the resin base material, forming a cured first layer 450 having theshape of where the photoinitiator was deposited. The resin-basedingredients of the resin base material combined with the photoinitiatorultimately yield a photoreactive resin shape at the precise locationswhere the photoinitiator was deposited/jetted. After the initial layer450 is formed on the build platform 460, the build platform 460 is moveddown into the vat material (first composition 415) as indicated by arrow465. The dispensing and light-exposing steps are then repeated to createanother layer of the part.

FIG. 4B shows the build platform 460 in a more submerged position thanin FIG. 4A to enable another layer 455 to be jetted and cured onto thealready-formed first layer 450. The distance that the build platform 460is moved and settled on corresponds to the thickness of the part layersbeing created. In embodiments, the build platform 460 may first movedown farther than the distance of a layer thickness, such as to mitigatebubbles or to allow vat material to be replenished for the nextdispensing iteration, and then move back up to settle in its desiredposition. After the layer 455 is cured, the steps of moving the buildplatform 460 down further, dispensing the second composition, and curingthe first and/or second compositions are repeated until the entireadditive manufactured part has been completed.

Embodiments disclosed herein, and particularly the dispensing head arrayand light source array embodiments of FIGS. 2-3, enable a 3D print jobto be performed at extremely fast rates and at much higher resolutionsthan traditional projection-based or SLA-based approaches. For example,embodiments can provide print rates up to 100 times faster than thesetraditional approaches, with resolutions comparable to 2D inkjet printerresolutions (e.g., 2400 dpi (dots-per-inch) or more). In someembodiments, multi-pass dispensing can extrapolate beyond such ranges.

Another advantage of the systems and methods of the present disclosureis enabling a 3D print build area to be increased in size whileachieving high resolution and without compromising build speed. Bytaking the photoinitiator out of the resin material, a vat-based resinmaterial is created that is very stable. Such resin base materials canbe exposed to light and not cure, thereby improving shelf life andeasing the ability to store the resin base material.

Methods for precisely dispensing the photoinitiator or other substancesmay include technologies used to deposit ink on paper in the 2D printingspace. Examples include thermal inkjet-based technology and piezo-basedjetting technology. Conventionally, inkjet and piezo-based jettingtechnologies are not capable of jetting highly viscous or high solidcontent materials that are used in additive manufacturing. However,embodiments of the present disclosure adapt these jetting technologiesfor dispensing certain jettable components of additive manufacturingmaterials such as photoinitiator solutions or other compounds that havelow enough viscosities that enable desired print speeds and printresolution to be achieved. Embodiments may also utilize other types ofdelivery systems for dispensing material onto a liquid substance in avat, such as using syringe-type pumps to dispense droplets.

The photoinitiator (or other substance for the second composition) isjetted at inkjet resolutions in the shape pattern (i.e., resolutions inthe X-Y plane per the coordinate axes annotated in FIG. 1) of each layerof the desired printed part, and then a light source (UV or otherappropriate wavelength) exposes the layer to illumination whichselectively cures the locations where the photoinitiator was preciselydeposited. Placing the photoinitiator at the surface of the resinmaterial in the vat very precisely enables materials that conventionallyhave very high cure-through to be printed accurately. Cure-through isthe amount of unintended curing that takes place in the next layer(Z-direction per the coordinate axes annotated in FIG. 1) beyond thecurrent layer being printed. By precisely controlling/depositing thephotoinitiator (or other reactant) on top of the surface as in someembodiments, the depth of cure is limited to the current layer beingaddressed. For example, inkjet drop sizes are on the order of 1picoliter (pL) to 2 pL, such as 1.2 pL to 1.5 pL, which are estimated inthis disclosure to be spherical drops of approximately 1.5 μm indiameter. These very small drop sizes result in extremely thin layerswhich translate into high resolution printed parts. Due to the reductionor lack of Z-compensation required in embodiments of the presentdisclosure, parts can be printed with high accuracy both in X, Y and Zdimensions. Another advantage presented by the present methods is thatsince the resin is polymerized from the top surface of the vat, theresin base material does not need to transmit light as much as in othervat-based systems, thereby widening choices of curing wavelengths andphotoinitiators that may be used.

In some embodiments, the resin base material in the vat can be high inviscosity (e.g., gel or honey-type viscosity) compared to the jettedphotoinitiator (or other dispensed material as shall be described inmore detail below). This difference in viscosity may assist in achievinghigh resolution of the printed part due to the viscosity of the resinbase material deterring the lower-viscosity dispensed material fromspreading on the surface of the resin base material (in the X-Ydirection). In some embodiments, the surface energy of thephotoinitiator and the resin base material, and the interfacial energybetween the photoinitiator and the resin base material can prevent (orlimit) the photoinitiator from spreading out after it is deposited,thereby substantially maintaining the resolution of the printed pattern.In addition, photoinitiator droplets will not penetrate (diffuse) verydeep into the resin base material, thus also providing high resolutionin the Z-direction since the resin will polymerize only to a thicknesswhere the photoinitiator has diffused into the base resin.

Examples of photoinitiators that may be used in embodiments arebis(cyclopentadienyl) bis[2,6-difluoro-3-(1-pyrryl)phenyl] titanium(CAS® Registry number 125051-32-3); 2,4-diethyl-9H-thioxanthen-9-one(CAS #82799-44-8); and diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide(CAS #75980-60-8). Examples of solvents for the photoinitiators, todispense the photoinitiators as a liquid solution, include ethylacetate, butyl acetate, isopropanol, 2-pyrrolidinone, and1-methyl-2-pyrrolidinone. In some embodiments, the dispensed material(e.g., photoinitiator solution) can have a viscosity of about 0.1centipoise (cP) to about 2 cP. For example, the viscosity of aphotoinitiator dissolved in ethyl acetate is about 0.42 cP. In someembodiments, the resin base material can have a viscosity of about 100cP to about 2700 cP, or more than 2700 cP. Accordingly, in someembodiments a difference in viscosity between the vat material (e.g.,base resin) and the dispensed material can be at least 10 cP, such asmore than 100 cP or more than 1000 cP or more than 2000 cP.

In addition to the viscosity of the drops, print resolution can also beaffected by reaction kinetics which can be controlled by the drop sizeand drop velocity of the dispensed material. This applies to anycombination of substances being used as the first composition and secondcomposition, not only to photoinitiator/base resin systems. For example,drop size affects the amount of substance that is involved in thereaction, and dispensing velocity affects the size of the dispersionarea that the droplet will create. Dispersion is a function ofviscosity, velocity, and mass of the droplet, as these aspects affectmomentum energy. Thus, dispensed drop size and dispensed drop velocityare two additional variables that can be used to adjust reactionkinetics and consequently control print resolution. Furthermore, thediffusion rate and reaction rate of the droplet's reactant (e.g.,photoinitiator or other substance as shall be described below) with thevat material can also be controlled by the chemistry of the reactant (esolubility, chemical affinity, etc.).

The size of a voxel (grid volume element of a 3D printed part,equivalent to a pixel in 2D printing) in embodiments of the presentdisclosure is related to many factors such as the relative viscositybetween materials in the volume, size of the dispensed droplets,diffusion/partition/chemical affinity of the ingredients in the droplet,wetting/surface energy of the dispensed material and vat material, timeelapsed between the subsequent drop addition (e.g., if multiplecomponents are being dispensed onto the resin in the vat), time elapsedbetween the droplet deposition and the application of UV radiation, andthe characteristics of the UV radiation. In the presentvat-based/dispensing systems, reactions are dependent upon mixing of allreactants. The dispensed substance(s) may be deposited simultaneously orsequentially, and reaction variables for controlling the resolution andother properties of the printed part include: (1) physics and/orchemistry of the droplet and the material in the vat, in whichviscosity, chemical affinity, and solubility are variables in diffusionof components from one place to another; (2) the manner of how thedroplets are deposited, where variables can include drop size, dropvelocity, dispensing sequences, and time between each drop sequence; (3)the manner of how the reactions are triggered, such as sensitivity ofthe photoinitiator to the UV wavelength and intensity, and sequence ofhow the UV light is used (wavelengths, intensity, sequence+time durationof the application). Factors related to controlling both the dispensing(jetting) and curing (e.g., UV light exposure)—such as specifying thedispensing time, the dwell time to allow dispensing components to mixwith components in the vat, and the curing light source behavior allwork together to achieve the desired properties of the 3D printed part.

In some embodiments, a dispensing and curing timetable can be utilizedto control the additive manufacturing system. In an example in whichphotoinitiator is dispensed, since curing can only occur when thephotoinitiator is present and activated by UV light, dispensing ofindividual resin components can be on a timetable designed for thedesired physical properties and structures. As an illustrative exampleof a timetable in which time units can be microseconds, milliseconds,seconds, or other: component A may be dispensed at time=0.0, component Bdispensed at time=2.1, component C dispensed at time=5.5, andphotoinitiator dispensed at time=7.6. This programmed timing betweencomponents A-C and the photoinitiator may be designed for specificchemical dwell/diffusion times between components. Continuing with thisillustrative example, UV light may be flashed at time=9.9 to 15 topolymerize the components and underlying vat material. Then component Dmay be dispensed at time=15.1 and UV light flashed at time=17.0, suchthat component D is polymerized into the layer as well.

FIGS. 5A-5B illustrate another advantage of the present embodiments,which is the ability to change the amount (e.g., different size drops,or different number of drops) and type of dispensed material (secondcomposition) that is deposited (e.g., jetted) onto different areas of alayer to address issues such as thermal effects. In conventionalprojection/LCD-based 3D print systems, printing is intentionally sloweddown to deal with thermal issues at a layer perspective. Slower printingnegatively affects throughput and increases costs. In some embodimentsof the present disclosure, the amount of second composition can beadjusted in specific areas, such as applying less photoinitiator inhotter regions to keep temperatures (e.g., as monitored by real-timemeasurements) normalized across the vat, thus mitigating the need toslow down print rates. This contrasts to conventional resins in whichthe amount or concentration of photoinitiator is homogenous, being veryconstant throughout the resin in the vat.

FIG. 5A is a plan view of a desired layer shape 550, such as shapes 150and 250 of FIGS. 1-2. FIG. 5B is a plan view of the second compositiondispensed in the desired shape onto the first composition 515 in a vat510. An outline of build platform 560 within the vat 510 is also shown.Regions 582 a (upper row) and 582 b (second row) illustrate differentconcentrations of the same drop size within the layer shape 550, wherein region 582 a there are fewer drops (represented by circles) than inregion 582 b (more drops in an equivalent space), resulting in a higherconcentration of the second composition in region 582 b. Regions 584 a-dillustrate different concentrations and different drop sizes within thelayer shape 550. For example, in region 584 b (bottom left darkrectangle) the drop sizes are smaller and much more numerous than inregion 584 a (row just above region 584 b). In region 584 c (upper rightarea) the drop sizes are larger than in region 584 b but smaller than inregion 584 a, and the density of drops per area is also in between thatof regions 584 a and 584 b. Region 584 d (adjacent to the left side ofregion 584 c) has a drop size and a density of drops per area that isdifferent yet from regions 584 a-c. These variations in drop size andconcentrations show how print properties can be tailored within a layerof an additively manufactured part by the dispensing process.

In further embodiments, thermal issues can be mitigated using techniquesin conjunction with or instead of controlling dispensing parameters. Forexample, real-time thermal measurements of the top surface of the vatmaterial can be employed to determine print delays and Z-axismoves/distances to allow resin to cool. Z-axis moves can be beneficialin high print density areas, since high print density areas can resultin high local temperatures. These motions in the Z-direction can bereferred to as “dip” moves and are greater in magnitude than a layermove (which moves a distance of the layer thickness). That is, a dipmove can move a distance beyond the thickness of a layer in order toallow the previously exposed layer to cool.

FIG. 6 is a flowchart 600 representing methods of the present disclosurefor creating additive manufactured parts, in which a photoinitiatorsolution is dispensed onto material in a vat. Step 610 involvesproviding a base resin in a vat, where the base resin has a firstviscosity and is absent of a photoinitiator. In step 620, a buildplatform is placed in the vat, submerged under a top surface of the baseresin. The build platform may be placed adjacent to and submerged justunderneath the top surface when the first layer of a part is formed, andthen submerged further into the vat as subsequent layers are formed onthe first layer. In step 630, a photoinitiator solution is dispensed onthe top surface of the base resin, the photoinitiator solution beingdispensed in a shape area according to a part to be created. Thephotoinitiator solution has a second viscosity that is less than thefirst viscosity of the base resin. Step 640 involves illuminating thetop surface to expose the photoinitiator solution and base resin tolight having a polymerization wavelength, where the light causespolymerization only where the photoinitiator solution was dispensed.After illuminating the top surface of the base resin to the light, step650 may involve moving the build platform down into the base resin andrepeating the dispensing step 630 and the illuminating step 640 tocreate another layer of the part.

For the flowchart 600, in some embodiments, a difference between thefirst viscosity and the second viscosity may be at least 10 cP. In someembodiments, the dispensing in step 630 may include varying aconcentration of the photoinitiator solution in different portions ofthe shape area to vary a property within the part, where theconcentration may be varied by varying a density of droplets per area ora dispensed droplet size of the photoinitiator. In some embodiments, thedispensing may include jetting. In some embodiments, the dispensing mayinvolve dispensing a material property modifier in at least a portion ofthe shape area, where the material property modifier may be one or moreof a reinforcement agent, a microstructure modifier, a heat stabilizer,an aging stabilizer, and a fiber. In some embodiments, the dispensinginvolves adjusting the second viscosity of the photoinitiator solutionin different portions of the shape area. In some embodiments, themethods further include adjusting a time between the dispensing step 630and illuminating step 640 in different portions of the shape area.

While the disclosure above describes depositing a photoinitiator onto aresin base material that lacks photoinitiator, embodiments also includecombining other types of materials such as different combinations ofpolymerization reactants and additives, which shall be described belowin this disclosure. Embodiments and benefits of the base resin andphotoinitiator systems described above apply also to other combinationsof vat materials and dispensed materials described throughout thisdisclosure. For example, dispensing a substance onto a vat-basedmaterial enables build areas to be increased in size while stillachieving high resolutions and print speeds. High resolutions in X-Y aswell as Z-directions can be achieved using dispensing methods such asinkjet technologies. Having polymerization occur at the top surface ofthe vat enables a wide range of vat materials to be used, since the vatmaterial does not have to transmit the polymerization wavelength.Separating polymerization components from each other—in the dispensedand/or vat material—can increase shelf life of the component materials.Thermal issues can also be mitigated by embodiments of the presentdisclosure. Another advantage of dispensing a material onto a vatmaterial is that properties can be varied within the produced part byvarying dispensing parameters within a layer. Reaction variables of thedispensed materials and vat material may be customized to achievedesired reaction kinetics, properties of the produced part, and degreeof curing in the part. Viscosity differences between the firstcomposition (vat material) and the second composition (dispensedmaterial) may be at least 10 cP, such as more than 100 cP or more than1000 cP or more than 2000 cP.

An embodiment of utilizing combinations of other types of polymerizationmaterials is for facilitating thiol-ene chemistry in a vat-typepolymerization vessel. FIGS. 7A-7B describe known thiol-ene chemistry inwhich thiol-ene polymers are formed by the reaction of -enes (e.g.,(meth)acrylate) with thiols. In FIG. 7A, a thiol is combined with an enedouble bond to result in an addition product. The scheme of FIG. 7Bshows the propagation and chain transfer reactions in thiol-enepolymerization. In the addition step, thiyl radicals add across an enefunctional group via an addition reaction that generates a carbonradical. In chain transfer, carbon radicals abstract hydrogen from athiol functional group forming the anti-Markovnikov addition product anda thiyl radical. In homo-polymerization, carbon radicals add across anene functional group via an addition reaction that generates anothercarbon-centered radical. These reactions can be initiated by commonphotoinitiators used in the trade of UV cure, such as 3D printing viathe photopolymerization of “ene,” such as a (meth)acrylate.

Conventional thiol-ene monomer systems polymerize extremely rapidly andalso exhibit minimal inhibition by oxygen and other traditionalstabilizers. As such, thiol-ene systems can be rapidly polymerized withlittle to no inhibition period to form tack-free surfaces with lowconcentrations of photoinitiator and low irradiation intensities. Whilethis feature is ideal in formulating ultra-fast and energy efficientsystems, a drawback is that thiol-ene mixtures may exhibit poor shelfstability at room temperature. Unstabilized shelf lives of thiol-enesystems can be as short as a few hours with the some rapidlypolymerizing thiol-ene systems. Thus, thiol-ene chemistry in additivemanufacturing systems is not known to be practiced commercially for thisreason.

However, embodiments of the present disclosure beneficially provide away to independently add thiol to ene, or ene to thiol (or to othercomponents) by a reliable delivery system such as an inkjet (e.g.,scanning/raster or page-array) or similar delivery system. Each materialcomponent of the full additive manufacturing material (e.g., thiols,enes, initiators, inhibitors) can be delivered as required in prescribedlocations, timings, concentrations and compositions. In someembodiments, three reactants (thiol, ene, initiators) and one or morediluents are utilized to dissolve and/or adjust the concentration ofthiols and initiators. The diluents can be solvents or one of the enecomponents.

In a first example, thiol and initiator are put in one dispensing unitas the second composition (140, 240, 440 of FIGS. 1, 2, 4A-4B), with anene in the vat as the first composition (115, 215, 315, 415 of FIGS. 1,2, 3, 4A-4B). Reaction variables of polymerization, such as thediffusion rate of the reactants, the size and concentration of the drops(as described in relation to FIG. 5B), and the time allowed for thediffusion of the reactants (i.e., elapsed time between dispensing andcuring) may be customized to achieve desired properties of the partbeing printed, such as a desired print resolution. In a second example,thiol is put in a first dispensing unit and the initiator is put inanother dispensing unit, and thiol and initiator are droppedsequentially onto ene in the vat. That is, the ene, in this secondexample is the first composition (115, 215, 315, 415 of FIGS. 1, 2, 3,4A-4B) and the thiol and initiator are second and third compositions(140, 240, 440 of FIGS. 1, 2, 4A-4B) that are dispensed. In this case,the size of the droplets (and thus the resulting voxels) may be setdepending on the diffusion rate of the reactants, as well as the timeelapsed between the thiol drops and the initiator drops. The ene mayhave a higher viscosity than the thiol and initiator in these twoexamples. That is, the vat material may have a higher viscosity than thedispensed material, as explained in relation to the photoinitiator andresin base material embodiments described above in this disclosure. In athird, more general example, the size of the voxels may be customizeddepending on the requirement of the end product. For a product requiringhigh resolution, the size and shape of the dispensed droplets can betuned to the required resolution. For example, a 1.5 picoliter drop isestimated to produce a 2 μm³ voxel. Furthermore, embodiments enable highresolution to be achieved consistently and at high production speeds inthe entire layer across the vat surface. In contrast, conventionalprojection-based systems can have high resolutions but focused on verysmall vat surface areas. Conventional lasers (e.g., for SLA) can havespot sizes of approximately 25 μm but would require very lengthy printtimes to achieve the same levels of resolution across an entire layerthat can be achieved by embodiments of the present disclosure.

Viscosities of the thiol-ene system components can be tailored accordingto the processing steps utilized, or to meet specifications of thefinished product, or to address resolution and thermal issues in variousembodiments. In general, the ene component has a higher viscosity thanthiol because it contains monomers and oligomers. In one example, anene+initiator component may be kept stable by storing it in the dark (asin conventional practice of photopolymerization materials), and thiscomponent's viscosity can be modulated by choices of ene formulation(where zero ene concentration means just initiator alone). In anotherexample, the viscosity of a thiol+initiator component can be modulatedby choice of thiol viscosity and solvent.

Further component mixtures for the vat material and dispensed materialmay be utilized, other than thiol/ene andphotoinitiator-less/photoinitiator combinations. A majority ofcommercial light cure resins are based on free radical curing acryliccompounds (acrylates), and thus acrylic-based compositions may beutilized in some embodiments, UV curable resins typically containoligomers, monomers, photoinitiator, and various additives such asstabilizers, antioxidants, plasticizers, and pigments. Any of theseresin components may be utilized in various combinations as the vatmaterial and dispensed material(s). Examples of oligomers that may beused in the present disclosure include aliphatic urethane diacrylate(e.g., EBECRYL® 4833) and hexafunctional aliphatic urethane acrylate(e.g., EBECRYL 5129), Examples of monomers that may be used in thepresent disclosure include aliphatic monofunctional diluting acrylate(e.g., EBECRYL 113), isobornyl acrylate, and dipropylene glycoldiacrylate. In an example embodiment, the resin component or thesustaining fluid in the vat (i.e., first composition) may have a densityof organic material of approximately. 0.95 to 1.20 g/cc. Combinations ofthese resin components (and additives as shall be describedsubsequently) may be utilized as the first composition for the vatmaterial and as the second composition for the dispensed materialsimilarly to the embodiments described throughout this disclosure forthiol-ene and photoinitiator-less resin/photoinitiator systems.

The viscosity of either the first composition in the vat or thedispensed second composition may be modified or customized to influencethe print process and final printed part. For example, the viscosity ofthe material in the vat may be customized to optimize both printabilityand desired product properties. The vat material may be formulated byjudiciously choosing a combination of all components to adjust theviscosity of the mixture in the vat. One example of tailoring theviscosity of the vat material without the use of any additive (e.g., athickener) is by considering the viscosities of individual components inthe resin mix and combining the components in appropriate proportions toresult in an overall viscosity of the composition. For instance, a firstcomponent with a viscosity μ1 could be combined in a particularproportion with a second component of viscosity μ2 to result in amixture that has a viscosity μ3 that is between μ1 and μ2. Anotherexample of adjusting the viscosity of the vat material is throughinteraction of special structures, such as hydrogen bonding andchelating. For instance, it is known that substances that have morehydrogen bonds, or that are capable of forming hydrogen bonds, tend tobe more viscous than those that do not. Studies in the industry havealso shown that cations chelation or the presence of NaCl can increasethe viscosity of a substance.

Another embodiment involving viscosity may include dispensing aviscosity modifier throughout the layer being printed or at selectedlocations, where the dispensing can vary (e.g., in drop size and/orconcentration as described in relation to FIG. 5B) within the dispensingpass. Because the dispensed material has low diffusion into the vatmaterial, the properties created in the printed layer due to the varyingviscosity can beneficially be customized in that specific print layer.Yet another embodiment may include modifying the dispensed material tobe more viscous at the outer perimeter of the dispensed area. This outerperimeter of more viscous material may help limit the amount ofdispersion of the photoinitiator or other dispensed component and mayresult in a more accurate surface finish of the additively manufacturedpart.

In further embodiments of vat material and dispensed materials, thematerial in the vat may be an inert medium in relation to polymerizationreactions, being a medium such as water, glycerin, or a gel. Thepolymerization components are then dispensed (as second composition 140,240, 440 of FIGS. 1, 2, 4A-4B) onto the inert medium (first composition115, 215, 315, 415 of FIGS. 1, 2, 3, 4A-4B). That is, the vat does nothave to contain reactant, it can be a non-solid medium to support thereactants. Using a thiol-ene system as an example, a minting sequencecan be to drop (dispense) ene, then drop thiol, then drop the initiatoron top of each other in a vat to create the thiol-ene-initiatorpolymerization, where the vat contains an inert medium such as water,glycerin, hydrocarbon oil, silicone oil or other. Attachment of thepolymerized layer to the build platform may be facilitated in someembodiments by, for example, doping the platform with a photoinitiatoror other polymerization reactant, or providing a surface treatment onthe build platform. The formulations in different areas or voxels of thepart's shape can be adjusted to achieve desired part properties such asa required print resolution as described herein, or to create unique 2Dor 3D microstructures, as shall be described in further detail below.

Embodiments may include injecting inhibitor material onto surroundingpattern areas of the part to be printed to prevent or control “X-YBleed,” which is diffusion and/or spreading of reactants within a layerof the printed part. This deposition of an inhibition material can beadvantageous from an accuracy perspective. Typically, if a partcontinues to cure (e.g., beyond the time of light exposure), X-Y growthoccurs, causing accuracy issues. By depositing a photoinhibitor at theborder of a shape area, the X-Y growth may be controlled by inhibitingcure beyond a certain boundary for optimal accuracy. A photoinhibitormay also be used to control cure-through (Z-direction) by depositing alayer of inhibitor on the surface of the vat material (which will becomethe down-facing surface of the subsequently-formed layer) before jettingthe other components. This deposition can be done during the printlayer, or after the cure before the components of the next layer aredeposited, for example during a recoating process.

Other embodiments may involve an inverse arrangement of the aboveembodiments. In these embodiments, a conventional resin is in the vat(including all the polymerization components such as photoinitiator),and then a pigment is injected (dispensed) on the surface of the resinmaterial to block the curing polymerization light. Alternatively, aphotoinhibitor may be dispensed on the surface of the resin material toprevent curing where the photoinhibitor is present. The pigment orphotoinhibitor is dispensed onto areas surrounding the shape of the partto be printed, rather than in the shape areas to be printed. When thesurface of the resin material is exposed to light (e.g., UV light suchas by scanning or a blanket exposure), the portions without the pigmentor photoinhibitor are cured into a layer of the additive manufacturedpart, while the pigment-coated or photoinhibitor-coated regions remainuncured. After the printed layer is cured, the build platform is moveddown in a layer move or dip move (distance greater than a layerthickness), which results in the pigment or photoinhibitor being mixedinto the general vat material. The next layer can then be formed, wherea fresh coating of pigment or photoinhibitor is dispensed onto areassurrounding the part shape of the next layer.

In some embodiments, a polymerization blocking material (e.g., pigmentor photoinhibitor) and a photoinitiator can be dispensed at differentlocations in the same layer of the part to be created. As illustrated inthe plan view of FIG. 8A of a top surface of a vat, photoinitiator 810(dark circles representing droplets) and pigment/inhibitor 820 (lightcircles representing droplets) can be jetted in selected locations. Theside cross-sectional view in FIG. 8B of a printed layer 840 depicts thelayer 840 after curing, in which peaks 812 are formed wherephotoinitiator 810 was deposited and valleys 822 are formed wherepigment/photoinhibitor 820 was deposited. That is, polymerization occurswhere the photoinitiator 810 was present, and polymerization isprevented where the pigment/inhibitor 820 was present. The precedingprinted layer 830 is also shown, which in this embodiment is solidacross the region on which the photoinitiator 810 and pigment/inhibitor820 drops were dispensed. The peaks 812 and valleys 822 create atextured surface similar to a hook-and-loop fastener material, which canimprove adhesion to the next layer of the printed part that will beformed on layer 840. In further embodiments, the photoinitiator 810 andpigment/inhibitor 820 can be dispensed in selected locations of a layerto create features such as voids within the part and textures on outersurfaces of the printed part.

Some embodiments include dispensing additives in addition to thereactant components that are needed to create the 3D printed part. Forexample, pigment, dyes, or other colorants may be deposited onto thesurface to create color objects. Examples of pigments include carbonblack, silicon dioxide, titanium dioxide and zirconium dioxide. Otherembodiments of additives include material property modifiers such asorganic or inorganic reinforcement agents (e.g., fibers), microstructuremodifiers, and heat and/or aging stabilizers for the finished parts.These additives may be deposited simultaneously with a reactant (e.g.,mixed with the reactant material) or subsequently (e.g., with a secondprinting head). Microstructure modifiers may use the kinetic and/orthermodynamic nature of modifier substances to create microstructures.In one embodiment, a modifier which will slowly react, dissolve ordeform prior to the photoreactivity fixation of the system may be usedto form a distinct microstructure in the body of the cured formation.For example, glycerol does not dissolve well in acrylic resin and can beused as a microstructure modifier by causing partial or no curing wherethe glycerol is present. In another embodiment, a modifier whichthermodynamically interacts with the structure of the resin, such as byhydrogen-bonding, van der Wools forces, or structure conformation willform a distinct microstructure in the body of the formation by modifyingthe mechanical properties of the part in that location. For example, ahydrophobic polymer can be injected (dispensed as the secondcomposition) into a hydrophilic resin (first composition in the vat),resulting in a thermodynamic force that will make the hydrophobic part(e.g., glycerol) curl up, thus creating a microstructure.

For dispensing multiple materials, such as reactants and/or additives,embodiments may include multiple printheads. FIGS. 9A-9C are plan viewsof example dispensers with multiple printheads, where the dispensers maybe, for example, inkjet or piezo-based jetting type, syringe/pump-type,or other. The print direction is indicated by arrow 970. Theseembodiments are illustrated as multiple printheads that move together ina single dispenser, such as to provide a larger area of dispensingcoverage to reduce print times. Embodiments also include providing theseprintheads in separate dispensing heads that can move independently fromeach other, such as for customizing the timing between when differentmaterials are dispensed. Other configurations of printheads as known in,for example, 2D paper inkjetting may also be utilized in embodiments ofthe present disclosure.

FIG. 9A shows a dispenser 901 for a raster scanning system (e.g.,dispensing head 120 of FIG. 1), in which each printhead 911 has twolinear arrays 915 of nozzles. Each printhead 911 may dispense adifferent material from each other. The three printheads 911 of FIG. 9Aare configured in an in-line array. That is, there is no offset betweenthe printheads 911, such that the printheads 911 print on the samelocation as the dispenser 901 moves. FIG. 9B shows a printhead 902 for araster scanning system, in which four printheads are configured in astaggered array. The printheads 912 a and 912 b are offset by adots-per-inch (dpi) amount 920 in the direction that the printheads willbe moved. With an offset being present, the offset and moving speed ofthe printheads determines a time between the materials being depositedonto the vat material (e.g., time between materials dispensed fromprinthead 912 a and printhead 912 b). This elapsed time betweendispensing materials can be used to customize reaction kinetics of thepolymerization, which can be used to customize properties of theproduced part such as voxel size. FIG. 9C shows a dispenser 903 for apage-wide system (e.g., dispensers 220 and 320 of FIGS. 2 and 3), wherethe printheads 913 are in a staggered array. The page-wide configurationof FIG. 9C can be used to increase additive manufacturing productionrates by dispensing material over a large area at once. In embodiments,a substrate (build platform) has a first reactant (vat material)covering the substrate, then additional reactants are dispensed by theprintheads of FIG. 9A, 9B or 9C (or other configurations of printheads)at desired locations on the build platform. The reactants need not bedispensed at all locations. For instance, if two additives are in theprintheads, both additives may be dispensed at some locations, while atother locations one or no additive may be dispensed.

FIGS. 10A-10H illustrate embodiments that include further configurationsof dispensing heads and illumination sources to enable customization ofproperties and characteristics of a printed part. The illuminationsources may also be referred to as light sources, curing sources orcuring heads. The illumination sources may be any light source thatproduces wavelengths of light for curing photoreactive polymermaterials. Examples of illumination sources include UV light-emittingdiode (LED) systems, UV flood lamps, mercury vapor UV bulbs, UVfluorescent bulbs, and projection-based systems. A raster-type scanningapparatus refers to a mechanism that moves side-to-side in one row andthen repeats this action in subsequent rows, resulting a back-and-forthX-Y movement. A page-wide scanning apparatus refers to a mechanism thathas a width in one dimension (e.g., X-direction) that covers an entirewidth of a layer to be printed (e.g., up to the entire width of a vatsurface), and then moves in the orthogonal direction (e.g.,Y-direction). Scanning speeds of the dispensing heads and illuminationsources may be, for example, 5 inches per seconds (ips) to 10 ips, or 10ips to 40 ips, or 1 ips to 60 ips. A blanket apparatus shall refer to astationary mechanism that covers the entire area of the layer to beprinted, such as up to the entire top surface of the vat. Othercombinations of the printheads besides those shown in FIGS. 10A-10H arealso included in the scope of this disclosure.

FIGS. 10A-10D demonstrate embodiments in which dispensing heads andillumination sources can be on the same or different axes as each other,or combinations thereof. FIG. 10A is a plan view of a top surface 1018of a vat 1010, with a raster-type scanning dispensing head 1020 a and araster-type scanning light source 1030 a moving on the same axis. Inthis embodiment, the light source 1030 a follows the dispensing head1020 a, where both move in a row in the X-direction and then proceed tothe next row to move again in the X-direction (movements indicated bythe arrows). This raster pattern continues until the dispensing head1020 a and light source 1030 a have passed over the entire area of vatsurface 1018 to be printed. In FIG. 10A the dispensing head 1020 a andlight source 1030 a move from right to left in each row, but otherembodiments can include moving from left to right in each row, oralternating right-left in one row and left-right in the next row (wherethe dispensing head 1020 a precedes the light source 1030 a in eachrow). FIG. 109 is a plan view showing a raster-type scanning dispensinghead 1020 b and a page-wide scanning light source 1030 b that are ondifferent axes from each other. Dispensing head 1020 b moves along a rowin the X-direction and then proceeds to the next row to move in theopposite X-direction. The light source 1030 b covers a width of the areato be cured, such as the full width of the vat surface 1018 in theX-direction in this embodiment, and thus only moves in Y-direction. FIG.10C is a plan view showing a page-wide dispensing head 1020 c and apage-wide light source 1030 c that both move along the same axis, beingthe X-axis in this embodiment. Only one pass across the vat surface 1018is needed for both the dispensing head 1020 c and the light source 1030c since the entire width in the Y-direction is covered by eachapparatus. FIG. 10D is a plan view showing a page-wide dispensing head1020 d and a page-wide light source 1030 d that move along differentaxes from each other. The dispensing head 1020 d moves along the X-axiswhile the page-wide light source 1030 d moves along the Y-axis.

FIGS. 10E-10H demonstrate embodiments in which a stationary blanketillumination source or projection-based illumination source projectsshapes or blanket images onto the layer being printed. The blanketillumination source or projection-based illumination source can becombined with a scanning raster-type dispensing head, a scanningpage-wide dispensing head, or combinations thereof. FIG. 10E is a sideview of a scanning dispensing head 1020 e (which can be raster-type orpage-wide) used with a stationary blanket curing illumination source1030 e. Illumination source 1030 e can be, for example, an array ormatrix of LEDs, or one or more UV flood lamps. Light 1032 emitted fromillumination source 1030 e covers an entire shape area of the part layerto be printed, such as up to the entire area of top surface 1018 of thevat 1010. FIG. 10F is a side view of a scanning dispensing head 1020 f(which can be raster-type or page-wide) used with a projector 1030 f.Projector 1030 f serves as a projection-based curing illumination sourcethat projects an image shape 1034. The image shape may be, for example,a bar, a line, or other shape that covers a portion of the print layerrather than the entire print area. As the dispensing head 1020 f movesover the vat surface 1018, the projector 1030 f causes the projectedimage 1034 to also move, following the dispensing head 1020 f. In oneexample where the dispensing head 1020 f is raster-type, the image 1034may be a square or circle that has a similar area or width (in thedirection perpendicular to the direction of scanning) as the dispensinghead 1020 f. In another example where the dispensing head 1020 f ispage-wide, the image 1034 may be a bar or line that is at least as wideas the dispensing head 1020 f.

FIG. 10G is a side view of a scanning dispensing head 1020 g(raster-type or page-wide) used with a projector-based illuminationsource 1030 g that projects a full image 1036 covering the entire layerbring printed on the top surface 1018 of the vat 1010. In someembodiments, the projected image 1036 may have the polymerizationwavelength across the entire surface, where curing on the surface occursselectively (in the desired shape areas only) due to the reactions ofthe dispensed and vat materials (e.g., where photoinitiator is presentwith a base resin, or where all polymer reactants are present). In otherembodiments, the image 1036 has the polymerization wavelength in theshape area to be printed, and non-polymerization wavelengths outside ofthe shape area. FIG. 10H is a side view of a scanning dispensing head1020 h (raster-type or page-wide) used with a projector-basedillumination source 1030 h that projects an image 1038 covering only thearea of intended cure. The image 1038 has the polymerization wavelengthand is a cross-sectional “slice” of the part to be printed. Thus, aslayers are formed in the vat 1010, the image 1038 changes according tothe shape of the particular layer being printed. The embodiments ofFIGS. 10G-10H may help to control X-Y bleed by reducing the dependencyof the timing between jetting and curing, since the top surface 1018 ofthe vat material is exposed to polymerization light only where the layershape is intended to be formed.

In summary, FIGS. 10A-10H describe embodiments in which variouscombinations of scanning raster-type dispensing heads, scanningpage-wide dispensing heads, scanning raster-type curing heads, scanningpage-wide curing heads, stationary blanket curing heads,projection-based illumination sources that project light in shapes thatmove over the surface, and projection-based illumination sources thatproject stationary images may be used. In addition to affecting printingspeed and controlling X-Y bleed, the various dispensing head andillumination source configurations may also be used to adjust theelapsed time between the dispensing (e.g., jetting) and curing (exposureof light on a particular region). The mechanical configurations ofdispensing and illumination apparatuses of FIGS. 10A-G (as well as FIGS.1-3) have a direct impact on the duration of exposure necessary toachieve a necessary energy to cause polymerization for a layer. Adesired amount of light exposure to cause polymerization may range from,for example, approximately 5 mJ/cm² to 20 mJ/cm² for a layer thicknessof 30 μm to 100 μm, such as 10 mJ/cm² to 20 mJ/cm² for a layer thicknessof 50 μm to 100 μm. The timing between dispensing and curing isdependent on the mechanical configurations of the dispensing and curingapparatuses, the spacing from the dispensing jet nozzles to the topsurface of the vat, and the speed of jetted drops (e.g., approximately 5m/s to approximately 20 m/s). The timing between dispensing and curingis also dependent on the dispensing head scan speed, which can rangefrom, for example, 5 ips to 60 ips if using speeds per 2D printingtechnologies. All of these factors may be customized in accordance withthe present disclosure to achieve desired reaction kinetics between thedispensed materials and vat materials.

Timing and curing power dependencies between i) the illumination sourceconfiguration and ii) the distance between the illumination source andtop surface of the vat material may also be utilized to customizeproperties and characteristics of the produced part. The illuminationsource configuration includes the power of the curing source.Embodiments may aim to keep a constant amount of time delay betweenjetting and curing over the entire vat surface. In one example involvinga scanning page-wide dispensing head and a scanning page-wideillumination source (e.g., light bar) that move along the same axis(e.g., FIG. 10C), a constant time delay between dispensing and curingmay be achieved by setting the moving speed of the illumination sourceto be equal to the dispensing head speed. The power level of theillumination source is then modulated to achieve a desired exposurerange. In a second example, a page-wide dispensing head is used withprojected light in the shape of a bar that chases the dispensing head(e.g., FIG. 10F). In this second example, the cure scanning speed is setequal to the dispensing bar speed, and power is modulated to achieve adesired exposure range. The width of the projected light bar (widthperpendicular to the length of the page-wide bar) is also a variablethat drives the power setting in order to maintain the constant timedelay between dispensing and curing. This second example may also applyto projecting sliced image data, such as in FIG. 10H, where theprojected light bar represents sequential linear strips of the slicedimage as the light bar moves across the surface.

In a third example involving blanket curing, as in FIG. 10E or 10G, thetime delay between dispensing and curing will vary across the surfacesince certain portions of the vat will receive dispensed materialsbefore other areas. In this example, the X-Y bleed may vary across theprinted layer, and diffusion of the dispensed material in theZ-direction (depth into the vat material) may also vary across thelayer. However, a trade-off between faster print speeds versus loweraccuracy (resolution) or less consistent mechanical attributes acrossthe layer may be acceptable for the part being produced such that theblanket curing is beneficial. In a fourth example, page-wide dispensingwith page-wide curing on a different axis as in FIG. 10D will also causethe elapsed time between dispensing and curing to vary across thesurface. As with the third example, the benefits of production speed inexchange for an acceptable level of print quality or mechanicalattributes may be acceptable. As can be seen by the embodiments of FIGS.10A-10H, the overall scanning speeds for the dispensing head andillumination source may be customized and determined by the type ofcuring source used, power emitted by the curing source, how the curingsource is configured relative to the dispensing head, and the distancebetween the dispensing head/light source and surface of the vatmaterial.

For dispensing fibers (e.g., carbon fibers, glass fibers) as anadditive, the size of the fibers can be appropriately sized for the typeof delivery system (inkjet nozzle, syringe-type, etc.). In someembodiments, the fibers may be included in the vat material rather thanin the dispensed material. In embodiments utilizing fibers, avat-based/dispensing system for additive manufacturing can be combinedwith an electric field system to control the orientation of the fibersduring print. FIGS. 11A-11B are isometric views of a system 1100 thatutilizes electric or magnetic fields. System 1100 includes a vat 1110, adispensing head 1120, an illumination source 1130, and an electric fieldapparatus 1180. Dispensing head 1120 may be configured as any dispensinghead described herein. Dispensing head 1120 deposits a secondcomposition 1140 on the surface of a first composition in the vat 1110,in shape area 1150. Illumination source 1130 may be configured as anylight source disclosed herein. The electric field apparatus 1180generates an electric field “E” (or magnetic field) in the vicinity ofthe vat surface, such as being configured as a plate, bar or apparatusof another shape that can be charged with a high voltage. The generatedelectric field is used to influence the orientation of fibers 1184, 1185with respect to the vat, where the fibers include an electricallyconductive or magnetic material such as carbon (e.g., nanotubes or otherallotropes) or metal. In some embodiments, the fibers 1184, 1185 may bemade of other types of materials such as glass, polymers, aramid,cellulose, biodegradable materials, bamboo, spider webbing, or blackwidow webbing, with the fibers being strategically charged electricallyor magnetically. Fibers throughout the system (vat material and/ordispensed material) may be charged with opposing polarities from eachother or may all be the same polarity.

In FIGS. 11A-11B, fibers are illustrated as being a component of thefirst composition in the vat 1110 but could also be dispensed as part ofsecond composition 1140 in other embodiments. Fibers 1184 are in theirnatural, disoriented state. In contrast, fibers 1185 are oriented in aparticular direction in response to electric field apparatus 1180passing over (in the print direction represented by arrow 1170) andbeing activated in certain regions (e.g., all or some of areas of theshape area 1150). Thus, methods include using the electric fieldapparatus 1180 to change an orientation of fibers to a desiredorientation in at least a portion of the part being created. In FIG.11A, the electric field apparatus 1180 is aligned along the length L ofthe vat 1110, such that the generated electric field E causes the fibers1185 to become oriented in the direction of the length L. In FIG. 11B,the electric field apparatus 1180 is aligned along the width W of thevat 1110, such that the generated electric field E causes the fibers1185 to become oriented in the direction of the width W. FIG. 11C showsan embodiment where more than one electric field apparatus is present.Electric field apparatus 1181 is aligned lengthwise while electric fieldapparatus 1182 is aligned widthwise, where the apparatuses 1181 and 1182can be activated and moved at different instances to achieve desiredorientations of fibers (e.g., at an angle that is non-orthogonal to L orW). In any of the embodiments of FIGS. 11A-11C, movements of theelectric field apparatuses can be linear, rotational, or otherdirections. The polarity and intensity of the electric field can also bechanged as the electric field apparatus moves across the vat, to createvarying properties in the layer of the formed part due to varyingorientations of the fibers. For example, the charge polarity can change,or the angle and/or orientation of the electric field can change.

FIG. 12 illustrates an embodiment in which fibers are caused to beoriented in a particular direction using kinetics/kinematics of nearbydroplets and/or by the chemical nature of the droplets. Such methodsinclude dispensing droplets to change an orientation of fibers to adesired orientation in at least a portion of the part being created. Thedispensing may include tailoring the droplet size, dispensing locationin the vat, droplet velocity and/or material being dispensed. FIG. 12 isa plan view of a portion of a top surface of a vat where fibers 1210 a,1210 b are illustrated as lines, and dispensed droplets 1220 areillustrated as circles. Fibers 1210 a are in their original“disoriented” position, and fibers 1210 b are in a desired orientationwhich is in the Y-direction in this illustration. The droplets 1220 maybe used to change the orientation of the fibers 1210 as indicated byarrows 1230, to be aligned with fibers 1210 b. The arrows 1230 show thefibers 1210 a being drawn (e.g., rotate) toward the droplets 1220 inthis embodiment, but the fibers could also be moved away from thedroplets. In one example, the kinetics/kinematics of a dispensed dropletimpacting the material in the vat may influence the orientation of afiber to change in a desired direction relative to the location ofdroplet impact. That is, the motion of the vat material caused by thedroplet falling onto the vat material can be used to modify the angle ofa fiber. In another example, the surface tension of a droplet 1220landing near a disoriented fiber 1210 a can be used to rotate the fibertoward the droplet, to be aligned with fibers 1210 b. That is, thepresence of dispensed droplets on the vat material changes the surfacetension of the surface of the vat material, thus causing the fibers tomove. This use of the dispensed material's surface tension property canbe employed as a chemical means of influencing the fiber orientation.Embodiments may include a vision capture device such as a camera 1240 topre-scan an area for disoriented fibers. This scanning information canthen be communicated to the dispensing head (e.g., jetting head) so thatdroplets are dispensed in strategic locations to control the orientationof the fibers in a desired manner.

Embodiments also include customizing properties such as color, flexuralmodulus, strength (e.g., tensile strength), and/or stability (e.g.,thermal, aging) in specific voxels of the printed part by using any ofthe embodiments described herein.

In some embodiments, properties can be controlled on a molecular scale.For example, by varying the concentration of the photoinitiator or otherdispensed substance from one drop to another in different parts of theprinted pattern, programmatic control over the number and length of thepolymer chains (and consequently degree of cure) in the final part canbe achieved. This customization is extremely desirable in 3D printing asit enables voxel-level control over physical properties of the printedpart, where voxel-level control can affect overall properties of thepart. As an analogy, a single large part behaves differently than abundle of small parts. In the same manner, voxel-level control ofmaterial properties can change the behavior of the overall part, such asin flexural modulus or tensile strength.

Embodiments can also control properties on a micro-scale, such as bycontrolling the concentration of a reactant via adjusting the size ofindividual drops of dispensed material and/or adjusting the density ofthe number of drops in an area. For example, if one region in a layerhas a high concentration of reactant while another low, the resultingprinted part will be a heterogenous structure instead of a homogenousstructure. This can be very advantageous from an advanced materialscience perspective involving microstructures, such as by enabling thebuilding of tessellated or regular physical patterns at the microscale.

In another example, properties can be controlled on a layer-by-layerscale, producing laminate structures of customized properties.Dispensing materials onto a vat can enable simulating a laminatestructure during print, where the structure is comprised of differentmaterials/ingredients to control different mechanical properties. Anexample application is for individualized dental aligners, which arecurrently not achievable by 3D printing. Embodiments provide the abilityto control properties such as flexural stress relaxation by adjustingthe sequence and concentration of dispensed material(s) onto a vatsubstance during the forming of simulated laminate structures. Flexuralstress relaxation is a key mechanical property for the dental aligneruse-case that addresses the requirement of having a low force that doesnot degrade over time under a load. The addressability that isachievable from jetting (or other dispensing method), along with theability to control concentrations of materials can help create differentflexural moduli at different positions during the print of a simulatedlaminate structure such as a dental aligner.

Macro-scale advantages can also be achieved by the shape and physicalproperties of the finished part, which can be determined by controllingthe overall reactions between the dispensed materials and vat-containedmaterials.

Embodiments furthermore enable physically challenging components to bedelivered and mixed on demand to prescribed reaction sites, Examples ofcomponents that are conventionally physically challenging to deliver arematerials with very high density (e.g., zirconium oxide or glass beads),which are difficult to disperse uniformly in a reaction medium sincethey tend to sink. Materials with lower density (e.g., polyethylene,wax, hollow spheres) than the reaction medium are also hard to disperseuniformly since they tend to gather toward an upper region of thereaction medium. These types of components can be deposited at desiredlocations within a printed part using the present methods and systems.For example, colloidal-type materials may be dispensed at specificregions as described in FIG. 5B, where instead of varying drop size orconcentration within a layer, the amount of dispersion particles beingdeposited may vary from region to region (e.g., no particles in someregions and some particles in other regions). Examples of dispersions ofparticles in liquids that may be used in various embodiments includeceramic matrices, ceramic slurries, inks with pigments, or minerals.Dental impression compounds are a specific example, which can includehigh loading of materials such as silicon dioxide or zirconium dioxidein (meth)acrylate resins.

For products requiring special microstructures or high production speed,larger drop sizes can be achieved by using dispensing methods other thansmall inkjet droplets. For example, a layered structure can be printedby depositing an entire layer of material instead of droplets. Inanother example, to print materials with a microsphere reinforcementstructure, the microsphere material can be interdispersed in the matrix(dispensed) materials and dispensed. Similarly, for printing a partreinforced with short fibers, the fibers can be interdispersed with, andthen dispensed with, the matrix materials.

FIG. 13 is a flowchart 1300 of methods for creating additivemanufactured parts in accordance with some embodiments, in which amaterial is dispensed onto another material that is in a vat. Step 1310involves providing a first composition in a vat, where the firstcomposition is a liquid with a first viscosity. In step 1320, a buildplatform is placed in the vat, submerged under a top surface of thefirst composition. The build platform may be adjacent to and justunderneath the top surface (e.g., upper surface of the build platformbeing 0 to 1000 μm below the top surface) when the first layer of a partis formed, and then submerged deeper into the vat as the followinglayers are formed on the first layer. In step 1330, a second compositionis dispensed on the top surface of the first composition. The secondcomposition has a second viscosity and is dispensed in a shape areaaccording to a part to be created. Step 1340 involves illuminating thetop surface to expose the first composition and the second compositionto light having a polymerization wavelength, thereby causingpolymerization of the first composition and/or second composition (i.e.,at least one of the first composition or the second composition). Afterthe illuminating step 1340, step 1350 may involve moving the buildplatform down into the first composition and repeating the dispensingand the illuminating steps to create another layer of the part.

For the flowchart 1300, in some embodiments the first composition is abase resin absent of a photoinitiator, and the second compositioncomprises the photoinitiator. In some embodiments, the first compositioncomprises a thiol or an -ene, and the second composition comprises the-ene or the thiol, respectively. That is, the first compositioncomprises a thiol and the second composition comprises an -ene, or thefirst composition comprises an -ene and the second composition comprisesa thiol. Other combinations of materials may be used for the firstcomposition and the second composition, such as various polymerreactants for the first composition and the second composition, whereadditives may be included in the first composition and/or the secondcomposition. Some embodiments may include step 1335 of dispensing aphotoinhibitor at a border of the shape area to prevent curing beyondthe desired shape area and thus improve dimensional accuracy of theproduced part. In some embodiments, the second viscosity of the secondcomposition is less than the first viscosity of the first composition.The dispensing of steps 1330 and 1335 may comprise jetting the secondcomposition from a printhead.

Some embodiments may involve a step 1325 of customizing a reactionvariable of the polymerization. For example, a reaction variable of thepolymerization may be customized to control a voxel size in the shapearea. A reaction variable of the polymerization may be customizedaccording to a desired property of the part to be created, the reactionvariable being chosen from the group consisting of: the first viscosity,the second viscosity, a chemical affinity between the first compositionand the second composition, and a solubility of the second compositionin the first composition. A reaction variable of the polymerization mayinvolve customizing an elapsed time between the dispensing step 1330 andthe illuminating step 1340 based on a desired property of the part to becreated. Step 1325 may be performed prior to the start of the entireadditive manufacturing print run or may be repeated during the print runto update the reaction variables in response to real-time feedback ofprinting parameters (e.g., vat material temperature, dimensionalmeasurements of the printed layers).

Further embodiments of step 1330 may include varying the secondcomposition in different portions of the shape area (e.g., to alterreaction kinetics), such as by varying the second viscosity or adispensed droplet velocity of the second composition. In someembodiments, the dispensing of step 1330 comprises varying aconcentration of the second composition in different portions of theshape area (e.g., to vary a property within the part), by varying adensity of droplets per area or a dispensed droplet size of the secondcomposition. In some embodiments, step 1330 may include dispensing athird composition on the top surface of the first composition in theshape area according to the part to be created, where the firstcomposition is an inert medium for polymerization, and the secondcomposition and the third composition are reactants for thepolymerization. In some embodiments of flowchart 1300, the dispensing ofstep 1330 involves dispensing a material property modifier (e.g., in thesecond composition or another dispensed composition) in at least aportion of the shape area, where the material property modifier may be areinforcement agent, a microstructure modifier, a heat stabilizer, anaging stabilizer, or a fiber.

Embodiments of the present disclosure advantageously enable mechanicalproperties within a part to be controlled based on varying positionalgradients of the dispensed materials, providing the ability to createvariable mechanical properties within a part. In one example, increasingamounts of photoinitiator can be deposited while progressing from oneside of the vat area to the other side over the given geometry shape ofthe layer part. Such a gradient in the amount of photoinitiator over thelayer can modify the mechanical properties by varying the degree ofcuring across the layer. Other ingredients can be dispensed in agradient manner as well, such as changing the concentration of adispensed monomer over the shape area to adjust mechanical properties.In another example, both a monomer and a photoinitiator can be dispensedin varying concentrations as the dispensing head is moved across the vatsurface. In various embodiments, the gradient in dispensing thematerials may be uni-directional, such as increasing from one side of alayer to the opposite side or decreasing from one side to the other. Inother embodiments the gradients may be multi-directional, such asincreasing partially across a layer and then decreasing, or varying intwo or three dimensions (e.g., X and Y instead of just X or just Y,and/or in the Z direction—see coordinate axes in FIGS. 1 and 2).

Yet further embodiments involve isolating one of the polymerizationcomponents within the vat material, such as by encapsulation or anemulsion, where the isolated component is released when exposed to anexternal influence such as light. In one example using photoinitiator asthe isolated component, the photoinitiator is encapsulated in shellsthat are distributed throughout the base resin. The shells can beselectively broken down with an external influence such as UV light or achemical that is jetted, thus releasing the photoinitiator and allowingtargeted curing. In such an example, methods involve providing a baseresin in a vat, where a photoinitiator is in a contained form in thebase resin; placing a build platform adjacent to and submerged under atop surface of the base resin; and applying an external influence to thetop surface of the base resin. The external influence is applied in ashape area according to a part being created, thereby releasing thephotoinitiator from its contained form and, upon exposure to lighthaving a polymerization wavelength, polymerizing the base resin in theshape area where the external influence was applied. The contained formof the photoinitiator may be particles encapsulated by shells. Theexternal influence may involve illuminating with UV light or jetting achemical.

Other embodiments include creating a product that can be foamed afterthe part is printed. Conventional foaming schemes have been practiced oncoatings on paper and in architectural materials such as wall panels andwall papers. Those coating materials contain chemical foaming agentssuch as ADCA (azodicarbamide, CAS #123-77-3), OBSH(4,4′-oxybis(benzenesulfonyl hydrazide), CAS #80-51-3) and DPT(N,N-Dinitrosopentamethylenetetramine, CAS #101-25-7). Chemical foamingagents are stable in fully polymerized acrylate coating systems (e.g.,paper coating and household paint). However, almost all of thecommercial foaming agents destabilize the acrylate monomers andoligomers for UV 3D printing systems. In some embodiments, the shelfstability issue is improved by dispensing the chemical foaming agentsonto a vat material, on demand at the right time, at the desiredlocation using the methods and systems described herein.

Reference has been made in detail to embodiments of the disclosedinvention, one or more examples of which have been illustrated in theaccompanying figures. Each example has been provided by way ofexplanation of the present technology, not as a limitation of thepresent technology. In fact, while the specification has been describedin detail with respect to specific embodiments of the invention, it willbe appreciated that those skilled in the art, upon attaining anunderstanding of the foregoing, may readily conceive of alterations to,variations of, and equivalents to these embodiments. For instance,features illustrated or described as part of one embodiment may be usedwith another embodiment to yield a still further embodiment. Thus, it isintended that the present subject matter covers all such modificationsand variations within the scope of the appended claims and theirequivalents. These and other modifications and variations to the presentinvention may be practiced by those of ordinary skill in the art,without departing from the scope of the present invention, which is moreparticularly set forth in the appended claims. Furthermore, those ofordinary skill in the art will appreciate that the foregoing descriptionis by way of example only, and is not intended to limit the invention.

What is claimed is:
 1. A method of creating additive manufactured parts,the method comprising: providing a first composition in a vat, whereinthe first composition is a liquid with a first viscosity; providing asecond composition to be dispensed, the second composition having asecond viscosity, wherein polymerization components for formation of alayer of a part to be created are separated from each other, and whereinat least one of the polymerization components is in the firstcomposition or the second composition; placing a build platform in thevat, submerged under a top surface of the first composition; duringformation of the layer of the part, dispensing the second composition onthe top surface of the first composition, the second composition beingselectively dispensed in a shape area according to a pattern area of thelayer of the part to be created; and illuminating the top surface toexpose the first composition and the second composition to light havinga polymerization wavelength, thereby causing polymerization of at leastone of the first composition or the second composition only in the shapearea where the second composition was dispensed.
 2. The method of claim1 wherein the polymerization components comprise a photoinitiator and abase resin absent of the photoinitiator, and wherein the firstcomposition is the base resin and the second composition comprises thephotoinitiator.
 3. The method of claim 1 wherein the polymerizationcomponents comprise a thiol and an -ene, and wherein the firstcomposition comprises the thiol or the -ene, and the second compositioncomprises the -ene or the thiol, respectively.
 4. The method of claim 1further comprising dispensing a photoinhibitor at a border of the shapearea.
 5. The method of claim 1 wherein the second viscosity of thesecond composition is less than the first viscosity of the firstcomposition.
 6. The method of claim 1 wherein the dispensing comprisesjetting.
 7. The method of claim 1 further comprising customizing areaction variable of the polymerization to control a voxel size in theshape area.
 8. The method of claim 1 further comprising customizing areaction variable of the polymerization according to a desired propertyof the part to be created, the reaction variable being chosen from thegroup consisting of: the first viscosity, the second viscosity, achemical affinity between the first composition and the secondcomposition, and a solubility of the second composition in the firstcomposition.
 9. The method of claim 1 further comprising customizing anelapsed time between the dispensing and the illuminating to customizereaction kinetics of the polymerization based on a desired property ofthe part to be created.
 10. The method of claim 1 wherein the dispensingcomprises varying the second composition in different portions of theshape area, wherein the varying comprises varying the second viscosityor a dispensed droplet velocity of the second composition.
 11. Themethod of claim 1 wherein the dispensing comprises varying aconcentration of the second composition in different portions of theshape area, by varying a density of droplets per area or a dispenseddroplet size of the second composition.
 12. The method of claim 1further comprising dispensing a third composition on the top surface ofthe first composition, in the shape area; wherein the first compositionis an inert medium for the polymerization; and wherein thepolymerization components comprise the second composition and the thirdcomposition.
 13. The method of claim 1 wherein the dispensing furthercomprises dispensing a material property modifier in at least a portionof the shape area, wherein the material property modifier is areinforcement agent, a microstructure modifier, a heat stabilizer, anaging stabilizer, or a fiber.
 14. A method of creating additivemanufactured parts, the method comprising: providing a base resin in avat, wherein the base resin has a first viscosity and is absent of aphotoinitiator; placing a build platform in the vat, submerged under atop surface of the base resin; during formation of a layer of a part tobe created, dispensing a photoinitiator solution on the top surface ofthe base resin, the photoinitiator solution being selectively dispensedin a shape area according to a pattern area of the layer of the part tobe created, wherein the photoinitiator solution has a second viscositythat is less than the first viscosity of the base resin; andilluminating the top surface to expose the photoinitiator solution andthe base resin to light having a polymerization wavelength, wherein thelight causes polymerization only in the shape area where thephotoinitiator solution was dispensed.
 15. The method of claim 14further comprising, after illuminating the top surface of the base resinto the light: moving the build platform down into the base resin; andrepeating the dispensing and the illuminating to create another layer ofthe part.
 16. The method of claim 14 wherein a difference between thefirst viscosity and the second viscosity is at least 10 cP.
 17. Themethod of claim 14 wherein the dispensing comprises varying aconcentration of the photoinitiator solution in different portions ofthe shape area, by varying a density of droplets per area or a dispenseddroplet size of the photoinitiator.
 18. The method of claim 14 whereinthe dispensing comprises jetting.
 19. The method of claim 14 wherein thedispensing further comprises dispensing a material property modifier inat least a portion of the shape area, wherein the material propertymodifier is a reinforcement agent, a microstructure modifier, a heatstabilizer, an aging stabilizer, or a fiber.
 20. The method of claim 14wherein the dispensing comprises adjusting the second viscosity of thephotoinitiator solution in different portions of the shape area.
 21. Themethod of claim 14 further comprising adjusting a time between thedispensing and the illuminating steps in different portions of the shapearea to customize reaction kinetics of the polymerization.
 22. Themethod of claim 1 wherein the illuminating exposes the entire topsurface to the polymerization wavelength.